In solder bonding for bonding electronic components to a substrate through solder bumps of a semiconductor package etc., the solder bumps are landed on electrodes of the substrate in the state in which a bonding paste (hereinafter simply referred to as “paste”) such as a flux or a soldering paste has been supplied to the solder bumps. In an electronic component mounting device for such electronic components to be mounted through solder bumps, a paste transfer unit for transferring a paste is disposed and the film thickness of a coating film formed on the paste transfer unit is required to be measured accurately in order to precisely adjust a transfer amount of the paste to each solder bump. Therefore, there has been disclosed a transfer unit using a system in which the film thickness can be measured automatically in place of a method which has been heretofore used to measure the film thickness by manual operation by means of a film thickness measuring jig (e.g. Patent Literature 1). In the conventional technique shown in the example of the Patent Literature, a film thickness measuring sensor is disposed above a peripheral position avoiding a transfer area to which a mounting head moves during transfer operation, so that the film thickness measuring sensor can be prevented from interfering with the mounting head which moves while holding electronic components in a space above the transfer unit.